The present invention relates to the field of plant molecular biology, particularly to the isolation of genes and their promoters. The invention further relates to the use of the genes and promoters to modify biochemical processes in plants.
Throughout their lives, plants are routinely subjected to a variety of stresses, which act to impede or alter growth and development processes. Stresses to plants may be caused by both biotic and abiotic agents. For example, biotic causes of stress include infection with a pathogen, insect feeding, and parasitism by another plant such as mistletoe, and even grazing by ruminant animals. Abiotic stresses include osmotic stress, excessive light intensity or insufficient light intensity, cold temperatures, warm temperatures, synthetic chemicals such as those used in agriculture, and excessive wind.
Because a stress negatively impacts plant growth and development processes, stress to agricultural plants has a negative economic impact expressed in the form of reduced yields, increased expenditures for pesticides or both. Developing crop plants that are better able to tolerate or even avoid stresses is desirable and will most certainly improve agricultural productivity. Given the world""s increasing human population and diminishing land area available for agriculture, improving agricultural productivity is a paramount challenge. A thorough understanding of the mechanisms used by plants to avoid or to tolerate stresses may help in the development of new strategies of improving the stress tolerance of agricultural plants.
In spite of the great frequency of stresses, plants survive, and often flourish. Plants are able to do this because of the evolution of a variety of internal and external mechanisms for avoiding or tolerating stress. For example, higher plants possess leaves with waxy, water-impermeable surfaces and pores known as stomata, which serve to allow the escape of water vapor during the process of transpiration. The periphery of the stomatal pores is lined with a pair of cells known as guard cells, which control the aperture of the pore. By modifying their size and shape through a turgor-pressure-mediated process, the guard cells can completely block the pore when conditions are unfavorable for transpiration during, for example, periods of low soil-water availability. Such a stress-avoidance system allows a plant to survive conditions of water stress by reducing transpiration to nearly zero and preventing dehydration.
Plants also possess defense systems for helping to limit the stresses resulting from attacks by pathogens and insects. One well-known defense system against plant pathogens is known as systemic acquired resistance. Another defense system is the systemic induction of proteinase inhibitors following insect damage, which is usually referred to as the systemic wound response. In both of these defense systems, the initial impact of the pathogen or insect is transmitted via a signal or signals to other parts of the plant which results in increased expression of genes encoding proteins that are directly or indirectly inhibitory to invading organisms. The associated, systemic increase in defense gene products is known to increase the resistance of the plant to both current and future stresses from pathogens and insects.
Despite the general similarities of the two systems, most of the components, such as signal molecules and defense genes, are distinct for the two defense systems. In systemic acquired resistance, salicylic acid is an important signal molecule, which acts to promote the resistance response in the plant. However, salicylic acid does not promote the systemic wound response, and in fact, there is some evidence to suggest that salicylic acid may act to repress the systemic wound response (Pena-Cortes et al. (1993) Planta 191:123-128; Doherty and Bowles (1990) Plant Cell Environ 13:851-858. Similarly, jasmonates are known to serve as signal molecules that promote the systemic wound response, but do not serve in a similar capacity in systemic acquired resistance.
The jasmonates are a group of naturally occurring molecules derived from the oxygenation of tri-unsaturated fatty acids and are distinguished by the presence of a cyclopentanone ring. Plants produce two of the most well-known members of the jasmonate family, jasmonic acid and its methyl ester, the perfume oil, methyl jasmonate. In plants, these compounds are synthesized from linolenic acid through a branch of a larger biochemical pathway known as the lipoxygenase pathway. This pathway was named for its first enzyme, lipoxygenase, which catalyzes the formation of lipid hydroperoxides from certain unsaturated fatty acids, which possess two or more double bonds. Because the predominant lipoxygenase substrates in plants are the eighteen-carbon fatty acids, linoleic acid and linolenic acid, the lipoxygenase pathway has been occasionally referred to as the octadecanoid pathway.
More recently, however, the lipoxygenase pathway has been referred to as the oxylipin pathway. Oxylipins, as their name implies, are oxygenated lipid molecules, which result from the oxygenation of unsaturated fatty acids via the lipoxygenase reaction and also include any molecules, irrespective of oxygenation status, derived from such oxygenated lipids. Given that jasmonates originate from the lipoxygenase-catalyzed synthesis of lipid hydroperoxides, they are oxylipins.
New strategies are needed for improving agricultural plants. While traditional plant breeding approaches will continue to be important for improving agricultural plants, the new strategies that are likely to have the most significant impact on crop improvement will involve genetic engineering.
Methods and compositions for expressing genes encoding homologues of Old Yellow Enzyme (OYE) are provided. The compositions comprise nucleotide sequences encoding monocot homologues of OYE, particularly those with a 12-oxo-phytodienoate reductase activity. The compositions further comprise antisense sequences of such nucleotide sequences. The sequences are useful in transforming plants for constitutive and stress-induced expression of sense and antisense sequences for homologues of OYE. Such compositions find use in methods for increasing stress resistance, modifying growth and altering oxylipin metabolism in plants.
Also provided are methods and compositions for regulating the expression of a nucleotide sequence in a plant in response to a stimulus. The compositions comprise promoters from genes encoding OYE homologues. Such promoters are useful in transforming plants for increasing the expression of a nucleotide sequence in response to a stimulus such as infection with a pathogen, insect or nematode feeding, and application of jasmonic acid and osmotic stress. Such sequences find use in increasing the resistance of plants to pests and pathogens and as well abiotic stresses.
Expression cassettes comprising sequences of the invention are provided. Additionally provided are transformed plants, plant tissues, plant cells and seeds thereof. Isolated proteins encoded by the sequences of the invention are provided.